Mobile concrete mixers



Sept. 28, 1965 E. WOLFF MOBILE CONCRETE MIXERS 3 Sheets-Sheet 1 FiledAug. 16, 1961 Sept. 28, 1965 E. WOLFF MOBILE CONCRETE MIXERS 3Sheets-Sheet 2 Filed Aug. 16, 1961 Fig.2

m w Q a 1 MW} U 1 7'17 2 N 7 R i M7 .|l W 0% mm Sept. 28, 1965 E. WOLFFMOBILE CONCRETE MIXERS 3 Sheets-Sheet 3 Filed Aug. 16, 1961 Fig.5

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INVENTOR. ZRAAYT W04 FF an ?AW United States Patent Office 3,208,735Patented Sept. 28, 1965 3,208,735 MOBILE CONCRETE MIXERS Ernst Wolff,Georgstr. 17, Detmold, Germany Filed Aug. 16, 1961, Ser. No. 131,792 8Claims. (Cl. 259-161) The invention relates to improvements in mobileconcrete mixers.

Mobile concrete mixers are known having tiltable mixing drums which arebasically hollow cylindrical in shape and are provided with a taperedconstriction, such drums requiring different filling, mixing anddischarge positions with regard to their axis. Mixing drums are alsoknown which likewise use the free-fall mixing action but in which thefilling and mixing positions are identical, and in this case the mixingdrum, with the mixing tools mounted in its interior, rotatessubstantially about a horizontal axis.

Furthermore, mobile concrete mixtures have already been proposed with avertical arrangement of the axis of the mixing drum and a concreteinstallation in the interior of the mixing drum, as a result of which anannular mixing chamber is formed. This known construction uses astationary drum with blade arrangements rotating about the axis of themixing drum. The blades are driven by a geared engine, which is in theinterior of the concentric installation, and move in the interior of theannular mixing chamber. This concrete mixer therefore uses a non-liftmixing action and in comparison with the ordinary tilting drummixer, itaifords an appreciable reduction in the mixing time and hence aconsiderably higher hourly output of fresh concrete. In practicaloperation, however, there is a greater Wear of material as a result ofthe rotating blades in the interior of the mixing chamber and allowanceis made for this by the provision of wearing plates. In this case, thewhole mixing chamber of the drum is lined with wearing plates which haveto be replaced frequently.

According to the present invention a mobile concrete mixer comprises aframe, a circular section mixing drum mounted on the frame and having asubstantially vertical axis, a tubular member disposed within the drumconcentrically therewith to define an annular mixing space, stationarymixing devices disposed in the annular space and means for rotating thedrum about said axis.

With this arrangement, the mix is constantly moved by centrifugal actiontowards the outer wall of the mixing drum where it is caught by thestationary mixing tools. In this process there is no substantialrelative speed between the mixing drum and the mix because the latter isentrained by the mixing drum and rotates. Wearing plates are thereforeunnecessary because the natural Wear remains within acceptable limits.

Preferably the drum is formed with a centrally disposed outlet in thefloor thereof and said tubular member is mounted for displacement from alower position in which it isolates said annular mixing space from saidoutlet to a raised position in which said annular mixing pacecommunicates with said outlet.

It is advisable for at least two mixing devices to extend into theannular mixing space which tools are articulated for horizontal pivotingon vertical bearing columns which are mounted outside the mixing drum,the distance between the mixing devices and the cylindrical inner wallof the mixing drum being adjustable. Following the idea of theinvention, each mixing tool comprises two vertically orientated bladeplates which face in different directions, one of which runs like achord in the mixing drum while the other has a direction which liesbetween the radial direction and that of the first blade plate, and thesecond blade plate ends above the floor of the mixing drum at a distancetherefrom while the first blade plate ends close to the floor of themixing drum. As a result of this formation of the mixing tools, combinedwith the centrifugal action exerted on the mix, an excellent andintimate mixture is obtained which not only improves the quality of theconcrete but also leads to an optimum mixing time which is considerablyshorter than the mixing times of known concrete mixers.

In order to prevent wear on the mixing tools, it is an advantage for thevertical leading edge considered in the direction of rotation of thedrum and/ or the bottom edge of the first blade plate to be covered witha protective layer of a resilient material, preferably rubber. Thisprevents the mix contacting the metallic edge of the mix ing tool andwear is eliminated at the stressed edges of the mixing tools. Even theprotective layer is exposed to only a little wear, because the parts ofthe mix which impinge on the layer bounce back as a result of theresilience of the latter so that there is substantially no abrasivesliding between the mix and the layer. In addition, the protective layeracquires a protective layer of very fine particles of mix for it hasbeen found that these very fine particles do not bounce back off theresilient material but are applied to the stressed surfaces.

The arrangement of the mixing devices is preferably such that they areequi-angularly disposed about the drum axis. As a result, the forcesarising in the mixing drum as a result of the engagement of the mixingdevices in the mix, are symmetrical.

Following the idea of the invention, a baflle is arranged substantiallyin the extension of the first blade plate of a mixing tool and ispivotable about a fixed vertical pivot pin extending into the mixingdrum, which baffie extends as far as the floor of the mixing drum andco-operates with a second battle, which is likewise mounted for pivotingabout a fixed vertical pivot pin extending into the mixing drum andsituated close to the centrally disposed drum outlet which second baffielikewise extends as far as the floor of the mixing drum, in such mannerthat, on actuation of an operating lever, both battles are pivoted insuch a manner that the mix is conveyed to the drum outlet and at thesame time the length of tube is moved to its raised position and the mixis expelled.

In order to prevent the cement fed into the drum from forming dust it isan advantage for the first baffie to be formed with a slot having adirection of length extending substantially parallel to the floor of themixing drum. Mix passes through this slot and covers the cementintroduced into the drum as a result of which unwanted evolution "ofcement dust is inhibited. In order to avoid Wear, it is advisable toprovide the bottom edges of the bafiles and the vertical leading edge ofthe second battle with a protective layer of resilient material,preferably rubber.

A measured quantity of water is fed into the space between thecylindrical inner wall of the mixing drum and the first blade plate ofeach mixing tool, with the result that the mixing intensity isfavourably influenced because the water is not fed on to the mix but isconveyed into areas which are free of mix and which extend substantiallyas far as the bottom of the drum, as a result of which the water isdrawn under the mix. As a result of this measure, it is unnecessary tostir the water into the mix from the top downwards, a step which canonly be carried out with difficulty because of the different specificgravities. Thus a concrete mixer according to the invention avoids onedisadvantage of known constructions.

The cement may conveniently be introduced between the cylindrical innerwall of the mixing drum and the first baffle behind the neighbouringwater intake, considered in the direction of rotation of the drum. Inthis case, the supply of cement to the mixing drum is preferablyeffected from a closed container which is suspended in a weighing deviceand the delivery socket of which can be closed by a hinged valve,andto'which the cement is supplied through a pipeline with a flexibleconnection by a completely enclosed continuous conveyor which isautomatically stopped on reaching a pre-set weight. As a result there isa considerable saving in time because the container can be re-filledagain whilst mixing is being carried out in the drum.

It has been found that the quality of the mix can be improved by addingcement and water which are already mixed together; this may convenientlybe effected as a result of the fact that the imaginary extension of theaxis of the cement delivery socket and the imaginary extension of theaxis of the adjacent water supply pipe converge towards one another inthe delivery direction and intersect inside the mixing drum.

Aggregate, for example gravel, is preferably supplied by means of aconveyor belt to a feed hopper which is suspended in a second weighingdevice, and the delivery end of which can be closed by means of a hingedclosing device, the conveyor belt being stopped automatically when theweight of aggregate in the hopper attains a predetermined value. By thismeans, too, there is the advantage of a saving in time because the feedhopper is refilled with aggregate during the mixing and the correctweight of aggregate is available immediately after the emptying of thedrum.

An additional advantage is obtained as a result of the fact that thefeed hopper is preferably in the form of a truncated rectangularpyramid, the smaller base of which forms the delivery opening which canbe closed by means of a hinged closure which is preferably in two partsand the two halves of which are pivotally mounted on opposite sides ofthe delivery opening. The free edges of the closure halves, which areactuated by a lever system, come into sliding contact with one anotherand with the two opposite free walls of the feed hopper respectively. Incontrast to all the known closures for gravel bins or hoppers, thehinged closure proposed according to the invention cannot jam andpermits particularly easy operation. A lever is preferably articulatedto each half of the closure at the outside of the closure device, whichlever together with the corresponding lever on the opposite half of theclosure, is articulated to one arm of a two-armed lever which ispreferably articulated to the feed hopper and the other arm of which isarticulately connected to a lever system, one lever of which isarticulated to a bearing which is preferably secured to the feed hopperand this lever can be pivotally actuated for the opening and closing ofthe closure device.

For adaptation to various heights on building sites, it is advisable forthe mixing drum to be connected through a rolling-bearing ring mount toa substantially horizontal frame arrangement which also carries themixing tools,

the weighing devices with the associated cement container and feedhopper and the drive unit for the mixing drum, the frame arrangementbeing guided for lifting movement on a vertical guide structure which isrigidly connected to the chassis. It is further an advantage for thecement conveyor and the conveyor belt for aggregate to be supported forpivoting in the longitudinal direction of the chassis with theirdelivery ends supported on the guide structure, While variable-lengthpivoted supports are articulated in the vicinity of their charging ends,the other ends of the supports being pivotally connected to the chassis.

One embodiment of the invention will now be described by way of example,reference being made to the accompanying drawings in which:

FIGURE 1 is a somewhat diagrammatic side elevational view 'of a mobileconcrete mixer according to the invention,

FIGURE 2 is a plan view of the mixing drum,

FIGURE 3 is a vertical section through the mixing drum of FIGURE 2,

FIGURE 4 is a side view of a mixing tool seen in the direction A ofFIGURE 2,

FIGURE 5 is a side view of a baffle, and

FIGURE 6 is a side view of a further baffle seen in the direction B ofFIGURE 2.

The mobile concrete mixer of this example comprises a chassis having atorsionally rigid frame 1, a rigid rear axle arrangement with travellingwheels 2, 2 preferably having pneumatic tires, and a jointed cross-shaftfront axle arrangement with travelling wheels 3, 3' which are likewisepreferably equipped with pneumatic tires. This oscillating axlearrangement may, for example, be pivotally mounted, through bearingmembers 4 on trunnions 5 which are secured to the under portion of asteering bogie 6. The oscillating axle arrangement has recesses 7 inwhich a towbar is suspended during the transport of the concrete mixer.In the operating position of the concrete mixer as illustrated in FIGURE1, the towbar is removed. Moreover, when the concrete mixer is inoperation, the chassis 1 must be aligned horizontally both in thelongitudinal direction of the chassis and in the transverse direction ofthe chassis and this may conveniently be effected by means of woodenblocks which are carried with the mixer and which are placed, in thevicinity of the rear axle arrangement, under the chassis 1 which has previously been raised, for example with a winch. Instead of the woodenblocks, however, vertically directed lifting spindle arrangements whichare rigidly connected to the chassis 1 may be provided at suitablepoints on the chassis, each lifting spindle arrangements consisting ofthe threaded spindle, a threaded nut handwheel or crank fixed to thechassis, and a foot plate. The front axle arrangement which isconstructed in the form of an oscillating axle automatically adaptsitself to irregularities in the ground and therefore does not have to bealigned.

In the vicinity of the rear axle arrangement, the chassis 1 carries aguide structure 8- which is directed substantially vertically and whichis rigidly connected to the chassis. The guide structure 8 may, forexample, be of framework construction with alternating bracing andcontains two vertical guide rails 9 which are disposed opposite oneanother in the transverse direction of the chassis. Each guide rail 9 isof U-section, the open side of the U facing the interior of the chassis.Engaging in the guide rails 9 are rollers 10 which are components of ahorizontally aligned tubular frame 11.. The tubular frame 11 comprisesvertically directed tubes 12, each of which is adjacent to a guide rail9 and on each of which are mounted at least two rollers 10 which are atdifferent heights. The tubes 12 are braced in relation to one another ina suitable manner and in relation to the tubular frame 11, for exampleby means of tubular stays 13. At the lower end of the frame arrangement11, 12, 13, preferably in the central longitudinal plane of the chassis,there is mounted a rotatable roller or pulley 14 which is supported onthe tubular frame arrangement through bearing members 15. Another rolleror pulley 16 is mounted for rotation on the guide structure 8 in thesame plane. A cable 17, which is secured to the tubular framearrangement, is taken over the pulleys 14 and 16 and wound on a cabledrum 18 which is mounted for rotation on the guide structure 8. Rigidlyconnected to the cable drum 18 is a worm wheel 19 which cooperates witha worm 21 on a spindle 20. The spindle 20 is mounted for rotation in theguide structure 8 and has a crank handle 22 at its free end. By means ofthis crank handle 22, the tubular frame'arrangement 11, 12, 13 can bedisplaced vertically in relation to the guide structure 8. In FIGURE 1,the tubular frame arrangement is shown in its highest position; anordinary ratchet and pawl or detent device is provided inside the cabledrum 18 and prevents the tubular frame arrangement from moving downautomatically. The frame arrangement 11, 12, 13 is not limited to theuse of tubes as components but may be produced by using other suitablesections.

Rigidly connected to the tubular frame 11 is a base plate 23 whichcarries the lower ring 24 of a rolling-bearing ring mount arrangement.The upper ring 25 of this ring mount arrangement is securedconcentrically to the lower face of a cylindrical mixing drum 26. Thusthe mixing drum 26 is mounted for rotation about a substantiallyvertical axis. The mixing drum 26 has a centrally disposed outlet 27 inthe floor thereof which is circular and in which a length of tube 28- ofsuitable outside diameter engages. This tube 28 defines with the drum 26an annular mixing space. Mounted coaxially with the mixing drum 26 andabove the latter is the drive unit which com prises an electric motor 29with gearing 30 connected in front of it and which is coupled through aflange coupling 31 to the drive shaft 32 of the mixing drum. The driveshaft 32 extend-s through the outlet 27 and is connected, through abolted engaging dog arrangement 33 to a driving rod 34. This driving rod34 extends horizontally and diametrically below the outlet 27 and isbolted or riv'eted to the mixing drum 26 with the interposition ofliners 35 and of a frustoconical discharge funnel 36. The drive unit isflange connected to a pipe 37 which is rigidly connected by welding orflange-mounting to the tubular frame 11.

The drive for the rotation of the mixing drum 26 may alternatively beeifected by means of a drive unit (not shown) which is not centrallymounted but drives the mixing drum 26 through a pinion (not shown) andtoothed rim (not shown) which is arranged concentrically with the ringmount arrangement 25, 24. This type of drive is preferred for largemixer units.

The length of tube 28 which closes the bottom opening 27 extends over aportion of the height of the mixing drum and is rigidly connected to aguide disc 42 through drive rods 41 which extend diametrically throughthe length of tube 28. The guide disc 42 is guided for rotation anddisplacement in height on the drive shaft 32 of the drum and is formedat its circumference with a circular depression or groove in which aguide ring 43 engages. The guide ring 43 is arranged in this groove insuch a manner that rotation of the guide disc 42 is possible inside theguide ring 43 which for assembly reasons is preferably in two parts.Lifting rods 45, which each carry a pivot pin 46 at their upper ends,are articulated by means of pivot pins 44 which are secured,diametrically opposite one another, to the guide ring. Transmission rods47, which are rigidly connected to a pivot pin 48, for example bywelding, are articulated to these pivot pins 46. The pivot pin 48 ispivotally held in position by bearing members 49. The bearing members 49are in turn secured to a bearing plate 50 which is fixed to the gearing30. This bearing plate 50 carries another bearing member 51 to whichpivoted rods 53 are articulated at 52, which rods are articulatelyconnected, through a pin 54 at their other end, to an actuating rod 55.The actuating rod engages in a forklike manner round the drive shaft 32and is articulately connected to the pivot pins 46. A handle 56 isprovided at the free end of the actuating rod 55.

Rigidly connected to the pivot pin 48, for example by welding, areone-armed actuating levers 57 and 58, to the free ends of which arearticulated push-and-pull rods 59 and 60. The linkage described so faris illustrated in plan view in FIGURE 2 and in a side view folded intothe plane of the drawing in FIGURE 3.

The push-and-pull rod 60 is articulated to a lever 61 which is rigidlyconnected, for example by welding, to a pivot pin 62 which projectsvertically into the mixing drum 26. This pivot pin is pivotally mountedon the bearing plate 50 and carries a bafile arrangement 63 which isrigidly connected thereto, for example by welding, and which reachesdown to the bottom of the mixing drum. The baffle arrangement shown inside elevation in FIG- URE 5 is provided with a slot 64 which extendsparallel to the floor of the mixing drum. The other push-and-pull rod 59is likewise articulately connected to a one-armed lever 65 which isrigidly mounted, for example by welding, on another pivot pin 66 whichis likewise pivotally mounted on the bearing plate 50. The pivot pin 66is rigidly connected, for example by welding, to a second bafile 67which is shown in side elevation in FIGURE 6 and in plan view in FIGURE2, and from the plan view the curvature of this second baffle 67 can beseen. The bafile 67 likewise extends downwards as far as the floor ofthe mixing drum.

FIGURES 2 and 3 show the position of the linkage and of the baffies whenthe concrete mixer is in the operating condition and the bafiles are ina rest position. When the contents of the mixing drum are to bedischarged, the handle 56 is pressed down as a result of which not onlyis the length of tube 28 raised vertically through the lifting rods andthe guide ring 43 but also the one-armed actuating levers 57 and 58 arepivoted in such a manner that the baflles 63 and 67 come into theiroperative position shown in chain-dotted lines in FIGURE 2, through theagency of the pull-and-push rods 60 and 59. When the baffles are in thisoperative position, the baffle 63 guides the mix towards the baflle 67and the latter guides the fully mixed concrete to the outlet 27 where itis discharged. If the handle 56 of the actuating rod 55 is released, thelength of tube 28 drops under its own weight closing the outlet 27 andat the same time the bafiles 63 and 67 swing back into their restposition.

Vertical bearing columns 68 are secured, for example by flange mountingor Welding, to the tubular frame arrangement 11, being substantiallydiametrically opposite in relation to the mixing drum 26. A head piece69 is pivotally mounted on each bearing column 68 and carries acantilever arm 70 which extends substantially hori zontally. From eachcantilever arm 70, a link 71 extends vertically into the mixing drum andcarries a mixing device 72.

The mixing devices 72 extend vertically downwards to the floor of themixing drum. Each mixing device 72 comprises two blade plates 73 and 74which extend in different directions as is clear from FIGURE 2. The

blade plate 73 represents the rectilinear extension of the link 71 andis formed at its free end with a recess so that a projection 75 is leftat the bottom of the blade plate 73. Welded to the vertical edge of therecess in the blade plate 73 is the second blade plate 74 which does notreach down to the floor of the mixing drum. The first blade plate 73extends in the direction of a chord inside the mixing drum. The secondblade plate 74 extends away from the first blade plate 73 in thedirection of rotation of the drum and inwardly of the chord. In effect,it extends in a direction which lies between the radial direction andthat of the first blade plate. The distance of the mixing tool 72 fromthe cylindrical inner wall of the mixing drum 26 is adjustable by meansof a link 76 welded to each bearing column and disposed opposite to alink 77 welded to the associated head piece 69 and provided with athreaded bore into which is screwed a screw 78 which bears with the endremote from the screw-head against the link 76. As a result ofappropriate screwing of the screws 78, the distance between the mixingtool 72 and the cylindrical inner wall of the mixing drum is varied asdesired.

The leading vertical edge of the blade plate 73 considered in thedirection of rotation of the drum indicated by the arrow 79 and thebottom edge of the blade plate 73 are encased in a protective layer 80of a resilient material, preferably rubber. It is also possible,however, to provide only one of the said edges with rubber. The rubbercasing 80 may, for example, be provided on the blade plate 73 in themanner illustrated in FIGURE 2, that is to say the rubber is appliedlaterally to the face of the blade plate. It is also possible, however,to use seetional rubber, for example in the shape of a U or L and tocover the working edge of the blade plate with it.

A U-shaped rubber section protects the edge from wear on all sides. AnL-shaped rubber section should be provided in such manner that the onearm of the L-section bears against the blade plate and the other armengages over the working edge of the plate. A protective layer 81 and 82may also be provided for the baffles 63 and 67 respectively,corresponding to the rubber layer 80 described for the mixing devices.In this case, the rubber layer 81 for the baffle 63 merely engages roundthe bottom edge of this baffle, while the baffle 67 has its leadingvertical edge protected in addition to its lower bottom edge.

In the example illustrated, two mixing devices are providedequi-angularly spaced about the axis of the mixing drum. It is alsopossible, however, to distribute a larger number of mixing devices aboutthe axis of the mixing drum 26 and this may be advisable with largemixing drums.

The water necessary for the concrete is supplied to the mixing drumthrough water supply pipes 83 and 84 which are only indicatedsymbolically in FIGURE 2. As can be seen from the drawing, the water isfed into the compartments or spaces which are present between thecylindical inner wall of the mixing drum and the blade plate 73 of eachmixing device. The water supply pipes 83 and 84 unite, as can be clearlyseen for FIGURE 1, behind a common shut-off valve or gate-type shut-offvalve 85, which is represented symbolically in the drawing. Thisshut-off member 85 is downstream of a water meter 86 which isillustrated diagrammatically and to which the water flows through a pipe87 which is provided at its outer end with connecting means for ahosepipe in a suitable manner. The water meter 86 permits accuratesupervision of the water supplied to the mixing drum and it is possibleto set the amount of water supplied in advance in which case the supplyof water is automatically shut 011 through the shut-off member 85 when ameasured quantity of water has been provided. For this purpose, thewater meter 86 may be provided with an impulse line which actuates anelectrical drive to the valve stem of the shut-01f member 85 when ameasured quantity of water has been provided.

The cement is supplied between the cylindrical inner wall of the mixingdrum and the baflie 63, behind the adjacent water intake 84 consideredin the direction of rotation 79 of the drum. A cement container 88 isprovided which is suspended by means of pivot pins 89 in a weighingdevice 90 which is only illustrated symbolically in FIGURE 1. Thestationary parts of the weighing device are rigidly connected to thetubular frame 11 through the pipe 37. Mounted in the delivery socket 91of the cement container 88 by means of two pivot pins 93 is a hingedvalve 92. An operating lever 94 is secured to the one pivot pin 93. Atits upper end, the cement container 88 is closed by a cover 95 which issecured to the container by means of bayonet catches (not illus trated).Welded into the cover 95 is a connecting pipe 96 over the free end ofwhich is slid a flexible union 97 which connects the connecting pipe 96to the connecting pipe 98 of a fully enclosed continuous conveyor 99.The flexible union 97 is provided in order to enable an accurateweighing of the cement content of the container 88 to be carried out.The continuous conveyor 99 is preferably of rectangular cross-sectionand is centrally divided by a partition wall 100. This partition wallpasses through the whole length of the continuous conveyor 99 and endsin front of the guide rollers 101 for the conveyor chain 102 in eachcase. Shovel plates 103 are secured, with uniform spacing, to theconveyor chain 102 and supply the cement to the cement container 88 inthe conveying direction 104. The drive of the conveyor chain 102 iseifected by means of an electric motor 105, and its driven pinion 106,through a belt or chain 107 to the conveyor-chain drive pinion 108. Afeed hopper 109 is mounted at the lower end of the continuous conveyor99.

Because of the complete enclosure of the conveyor members, the cement issupplied to the cement container 88 without the formation of any dust.The drive motor is automatically switched 011 when a predeterminedweight of cement is present in the cement container 88 and measured bythe weighing device 90.

The water supply pipe 84 may be directed in such a manner (not shown)that entering water intersects or meets with cement passing through thecement discharge socket inside the compartment between the baffie 63 andthe cylindrical inner wall of the mixing drum. As a result, if water andcement are supplied simultaneously, the cement and water meet in thedrum and a mixing of these two materials takes place so that in effect,grout is fed into the mixing drum 26. For the sake of clarity, thecement container 88 with its operating members and the baffies 63 and 67are not shown in FIGURE 3. The mixing devices 72 are not fullyillustrated therein either and one mixing tool is merely folded into theplane of the drawing.

The aggregate for the concrete, for example gravel, is supplied to themixing drum 26 through a feed hopper 110 which is also suspended in aweighing device 111, indicated symbolically in FIGURE 1, through pivotpins 112. The feed hopper 110 and the weighing device 111 may be rigidlyconnected to the tubular frame arrangement 11, 12, 13 for examplethrough bracket 112a. The supply of aggregate to the feed hopper 110 iseffected by means of a conveyor-belt device 113 which comprises anendless conveyor belt 116 guided over guide rollers 114 and 115. Theconveyor belt 116 is driven by a drive pinion 117 of an electric motorwhich is not illustrated, through a chain or belt drive 118. The loadingof the conveyor belt 116 is effected in known manner through a scraperdevice of which the drive motor 119 and winch device 120 are secured tothe chassis 1. The cable 121 which is secured to the scraper and whichis wound on the drum of the winch device 120, is guided over pulleys 122and 123. The pulley 122 is held, through a pivot 124 by a bracket device125 secured to the chassis 1. The pulley 123 is adapted for pivoting inrelation to the bracket device 125 through a joint 126. The pivotalarrangement of the guide pulley 123 makes allowance for the variousangular positions of the scraper cable 121. The aggregate, for examplegravel, is supplied to the conveyor belt 116 by the scraper which isintroduced inside a guide plate device 127. The drive of the conveyorbelt 116 is automatically switched off as soon as a predetermined weightof aggregate is present in the hopper 110 as measured by the weighingdevice 111. Instead of the one conveyor belt 113, a plurality ofconveyor belts, for example three, may be provided to supply theaggregate to the feed hopper 110.

In order to produce a high-strength concrete, it is known that not onlythe proportion of the aggregate by weight to the total mix is importantbut also, particularly with gravel, the composition must correspond, asregards grain size, to a specific grading curve determined by previouscalculation. In order to ensure that the course of this grading curveis, in fact, in the favourable range in practice, the gravel isdelivered in separate specific grain sizes, for example in the grainsizes 0 to 7, 7 to l5, 15 to 30 mm. These various groups of gravel arethen combined in proportions by weight determined according to thegrading curve for each concrete mix. In the concrete mixer according tothe invention, the combination of the individual groups of gravel in amix can be effected by means of three conveyor belts. The first belt,for example, conveys only the grade 0 to 7 mm. and after the specificcalculated weight of this grade has been conveyed into the feed hopper,this conveyor belt is automatically switched off and the next conveyorbelt begins to supply another grade, for example with the grain size 7to 15 mm. The second conveyor belt is automatically switched off whenthe required Weight of the grade 7 to 15 mm. plus the weight of thegrade to 7 mm. already present has been reached in the feed hopper. Atthe same time, the third conveyor belt begins to supply the grade to 30mm. When the total weight of the aggregate with the grain sizes to 0 to30 mm. has been reached, the third conveyor belt is also switched offagain and after the feed hopper has been emptied into the mixing drum,the first conveyor belt again begins automatically to supply the grade 0to 7 mm. The automatic switching on and off of the conveyor belts isefretced by means of known and appropriate electrical circuit elements.

The feed hopper 110 is preferably in the form of a rectangular truncatedpyramid, the smaller base of which forms the delivery opening which canbe closed by a hinged closure 128, 129 which is preferably in two parts.The halves 128 and 129 of the closure are pivotally connected toopposite longitudinal sides of the delivery opening, for example bymeans of hinges 130. In the closed position, the longitudinal edges 131of the two halves 128 and 129 of the closure lie together, and theshorter edges 132 of the two halves of the closure lie against theopposite free side walls of the feed hopper 110. Mounted on each edge132 of the closure is a pivot pin 133 on which a lever 134 isarticulated. Each pair of adjacent levers 134 is articulated throughpivot pins 135 to the long arm 136 of a two-armed lever. The two-armedlevers are each pivotally mounted on the feed hopper 110 at 137.Articulated to the short arm 138 of the two-armed lever is anintermediate member 139 which is articulately connected to a lever 140which is rigidly connected to a tube 141, for example by welding. Thetube 141 is pivotally guided in brackets 142 on the feed hopper 110. Alever arrangement as described for the halves of the hinged closure isprovided on each of the narrow sides of the feed hopper. The tube 141 isprovided with an operating lever 143, on rotation of which the levers140 are pivoted in such a manner that the short arm 138 of the two-armedlever is raised as a result of which the long arm 136 of the two-armedlever moves downwards. In the course of this, the levers 134 swingoutwards and open the two halves 128 and 129 of the closure. When theclosure is in the closed position, the levers 140 bear against stops 144which prevent the hinged closure from opening automatically. Theconnecting members 139 are directed so that the moment of force exertedon the short lever arm 138 of the two-armed lever as a result of themoment of loading urges the levers 140 against the stops 144. Whenopening the hinged closure only a very slight force is necessary totransfer the levers 140 and the connecting members 139 to the other sideso that the halves of the closure open automatically under the action ofthe load.

Mounted for rotation inside the tube 141 is an actuating shaft 145 whichcarries a lever 146 at one end and an operating lever 147 at the otherend. The lever 146 is articulately connected to a transmission rod 148which in turn is articulately connected to the lever 94 of the hingedvalve 92 in the delivery socket 91 of the cement container 88. Onappropriate actuation of the operating lever 147, the hinged valve 92 isopened or closed.

The continuous conveyor 99 and the conveyor belt device 133 are suitablybraced together. The two conveyor devices are articulately supported bymeans of pivot pins 149 on a cross bar 150 connecting the two frametubes 12. Articulated substantially in the middle of the conveyor beltdevice 113 are pivoted supports 151, the other ends of which arearticulately connected to the chassis 1. These pivoted supports 151 formthe second support for the conveyor devices. The pivoted supports may beadapted for variation in length, for example, by means of a screwshackle 152. Thus it is possible to adapt the concrete mixer to thevarious build 10 ing sites as regards the height of the loading ends ofthe conveyor devices.

The mixing process of the concrete mixer is described below. The water,the cement and the aggregate, for example gravel, are supplied inpredetermined quantities by weight, to the mixing drum 26 which rotatesat 50 revolutions per minute. It is possible to plan in advance thequantities by weight of the mixture components to be supplied, as aresult of which the correct weights of charge are always presentautomatically. The mix introduced into the mixing drum comessubstantially against the cylindrical inner wall of the mixing drumunder the action of centrifugal force, and there it is caught by themixing devices and churned up. In the course of this, various componentsof motion are superimposed in the mix, being caused by the formation ofthe mixing devices in conjunction with the action of centrifugal force.Although the components of motion are discussed individuallyhereinafter, nevertheless it should always be remembered that thesecomponents of motion only appear superimposed on one another. The bladeplate 73 of each mixing device deflects the mix from the inner Wall ofthe drum against the action of centrifugal force. After passing theblade plate, the mix is again applied against the inner wall. Thus asubstantially radial reciprocating movement is imparted to the mix. Theproportion of the mix which comes into contact with the blade plate 74at first piles up, rises up this blade plate and tips over. On the otherhand, the mix can pass freely through the space below the blade plate 74and is merely influenced by the projection 75 on the first blade plate73. As a result of the arrangement of the blade plate 74, therefore,there is a relative velocity inside the mix which contributes veryconsiderably to the satisfactory intimates of the mixing. The intensityof the mixing of the mixing devices is so great that the mixing time isreduced to a minimum. The supply of the water and of the cement is veryimportant as regards the mixing operation and, as already mentioned,these reach the mixing drum substantially already in the form of grout.The water, as described, is introduced into those areas in which thereis no mix, that is to say the water reaches the bottom of the drum fromwhence it is constantly entrained by the rotating mix. It is thereforeunnecessary to convey the water below the mix, a step which is naturallydifiicult to carry out because there is a considerable differencebetween the specific gravity of water on the one hand and of the othercomponents of the mix on the other hand. The water which is suppliedthrough the Water supply pipe 84 and which becomes mixed with the cementsupplied through the cement delivery socket 91, is covered, immediatelyafter entering the space between the baffle 63, the one mixing tool 72and the cylindrical inner wall of the mixing drum, by mix which passesthrough the slot 64 in the baflie 63, so that any disturbingdust-formation in the cement which has not yet come into contact withwater is prevented. At the same time, however, the cement and the waterare constantly drawn into the rotating mix. The passage of the mixthrough the slot 64 is effected by the action of centrifugal force. Itis worth noting that relatively little water is used to mix the concreteand this is a direct consequence of the extremely thorough mixing. Inconsequence, no segregation occurs after the fully mixed concrete hasbeen laid by the builder, such as can frequently be observed in the formof a layer of water lying on concrete floors, and the concretestructures dry out very quckly. Thus the mixer according to the invention not only affords a reduction in the mixing times but also animprovement in the quality of the mix. In addition, it is worthmentioning that the charging times for the components of the mix arevery short because the cement container and the aggregate feed hopperare automatically re-filled during the mixing time which only lasts afew seconds. As a result, it is possible to charge the drum with freshcomponents of the mix again immediately after it has been emptied. Thefinished concrete flows over a guide 153 into a skip which is held inreadiness or may be supplied directly to a displacement-type concretepump.

In the concrete mixer described so far, all the moving devices of themachne are driven by electric motors. It is possible, however, toprovide a main drive, instead of these individual drives, and this maindrive may be mounted on the chassis 1. This main drive may convenientlyconsist of an internal combustion engine which drives the machinecomponents to be moved, through conventional transmission means such asshafts, gearwheels and belt or chain drives. When a main driveconsisting of an internal combustion engine is used, it is possible toadapt the concrete mixer so that it is self-propelled, thus renderingunnecessary the towing of the concrete mixer to the site by means of alorry or tractor. For transport, the tubular frame arrangement 11, 12,13 is lowered inside the guide structure 8 by means of the manuallyactuated worm drive 19, 21, until the lower surfaces of the tubularframe arrangement rest on the chassis 1 and the conveyor devices 99, 113are substantially horizontal in the longitudinal direction of thechassis. The conveyor devices then rest on the chassis through the pivotpins 149 and through the pivoted supports 151 and may be secured inposition by the provision of additional supports.

What I claim is:

1. A mobile concrete mixer comprising a frame, a circular section mixingdrum mounted on said frame and having a substantially vertical axis, anouter wall, and a floor having a centrally positioned outlet, a tubularmember concentrically disposed within said drum for defining an annularmixing space, means for moving said tubular member from a lowerposition, where it isolates said annular mixing space from said outlet,to a raised position, where said annular mixing space communicates withsaid outlet, a first baffle positioned in said annular mixing space andextending to the floors of said drum, means for mounting said firstbaffle for pivotal displacement about a substantially vertically axisfrom a rest position to an operative position in which said first bafileguides the concrete mix in said annular space toward said outlet, asecond bafile extending into said annular mixing space to the floor ofsaid drum, means for mounting said second baflle for pivotaldisplacement about a substantially vertical axis from a rest position toan operative position wherein said second bafile guides the concrete mixin said annular space towards said first baffle, stationary mixingdevices disposed within said annular space and being positioned alongsaid outer wall, and means for rotating said drum about said axis at aspeed suflicient for moving the concrete mix towards said outer wallunder the action of centrifugal force whereby said concrete mix iscaught and mixed by said mixing devices.

2. The mobile concrete mixer of claim 1 wherein the lower edges of saidfirst and second bafiles and the leading vertical edge of said firstbaffle are protected by a layer of 6 resilient material.

3. The mobile concrete mixer of claim 1, wherein a cement deliveryoutlet is provided for delivering cement to said drum at a locationbetween said second bafile and the outer wall of said drum.

4. The mobile concrete mixer of claim 3 wherein said second baffleincludes a substantially horizontal slot for permitting the passage ofconcrete mix therethrough.

5. A mobile concrete mixer comprising a frame, a

circular section mixing drum mounted on said frame and having asubstantially vertical axis and an outer wall, a tubular memberconcentrically disposed within said drum for defining an annular mixingspace, at least two stationary mixing devices disposed within saidannular space and being positioned along the outer wall of said drum, avertically extending bearing column associated with each of said mixingdevices and being disposed externally of said drum, means for connectingeach of said mixing devices to its associated bearing column for pivotaldisplacement about said column, and means for rotating said drum aboutsaid axis at a speed sufficient for moving concrete mix toward saidouter wall under the action of centrifugal force whereby the concretemix is caught and mixed by said mixing devices. 6. The mobile concretemixed of claim 5 wherein means are provided for displacing said mixingdevice relative to the outer wall of said drum and also wherein saidmixing devices are disposed substantially equi-angularly about the axisof said drum.

7. The mobile concrete mixer of claim 5 wherein each of said mixingdevices comprises two vertically extending blade plates, the firstextending in the direction of a chord of said drum and the second ofsaid plates extending away from said first blade plate in the directionof rotation of said drum and inwardly of said chord.

8. The mobile concrete mixer of claim 5 wherein said first blade plateextends substantially to the floor of said drum andsaid second bladeplate ends short of said floor and wherein the leading vertical edge ofsaid first blade plate is protected by a layer of resilient material.

References Cited by the Examiner UNITED STATES PATENTS 1,358,045 11/ 10Woodhull 25934 1,750,244 3/30 Robb 259154 1,767,809 6/30 OReilly 25988 X2,687,285 8/54 Fisher 259154 2,727,733 12/55 Carswell 259-154 2,739,7973/56 Kemper 259161 FOREIGN PATENTS 746,876 3/56 Great Britain. 853,44311/ Great Britain.

OTHER REFERENCES Engineering News, Dec. 12, 1912, page 1085, A ConcreteMixer of New Type.

WALTER A. SCHEEL, Primary Examiner.

LEO QUACKENBUSH, Examiner.

5. A MOBILE CONCRETE MIXER COMPRISING A FRAME, A CIRCULAR SECTION MIXINGDRUM MOUNTED ON SAID FRAME AND HAVING A SUBSTANTIALLY VERTICALLY AXISAND AN OUTER WALL, A TUBULAR MEMBER CONCENTRICALLY DISPOSED WITHIN SAIDDRUM FOR DEFINING AN ANNULAR MIXING SPACE, AT LEAST TWO STATIONARYMIXING DEVICES DISPOSED WITHIN SAID ANNULAR SPACE AND BEING POSITIONEDALONG THE OUTER WALL OF SAID DRUM, A VERTICALLY EXTENDING BEARING COLUMNASSOCIATED WITH EACH OF SAID MIXING DEVICES AND BEING DISPOSEDEXTERNALLY OF SAID DRUM, MEANS FOR CONNECTING EACH OF SAID MIXINGDEVICES TO ITS ASSOCIATED BEARING COLUMN FOR PIVOTAL DISPLACEMENT ABOUTSAID COLUMN, SAID MEANS FOR ROTATING SAID DRUM ABOUT SAID AXIS AT ASPEED SUFFICIENT FOR MOVING CONCRETE MIX TOWARD SAID OUTER WALL UNDERTHE ACTION OF CENTRIFUGAL FORCE WHEREBY THE CONCRETE MIX IS CAUGHT ANDMIXED BY SAID MIXING DEVICES.